U.S. patent number 7,918,304 [Application Number 12/399,071] was granted by the patent office on 2011-04-05 for steering assist for a rear caster wheel on a work machine.
This patent grant is currently assigned to Deere & Company. Invention is credited to Shirish Chobhe, Francine J. Perry, David V. Rotole.
United States Patent |
7,918,304 |
Perry , et al. |
April 5, 2011 |
Steering assist for a rear caster wheel on a work machine
Abstract
A steering arrangement for a work machine includes a frame, at
least one caster wheel assembly carried by the frame, at least one
turn assist cylinder, and a turn assist arrangement. Each turn
assist cylinder is coupled between the frame and a corresponding
caster wheel assembly. The turn assist arrangement includes a
steering assembly, a steering assist valve and a transfer gear. The
steering assembly includes an output gear which is positionable
dependent upon an operator commanded degree of turn. The output
gear has exterior teeth. The steering assist valve is configured to
selectively operate at least one turn assist cylinder and thereby
bias a corresponding caster wheel assembly during an operator
commanded turn. The steering assist valve includes an input gear
with exterior teeth. The transfer gear includes a first set of
peripheral teeth enmeshed with the output gear and a second set of
peripheral teeth enmeshed with the input gear. The transfer gear
pivots about a common pivot point. The first set of peripheral
teeth and the second set of peripheral teeth are each at a common
radius from the common pivot point on opposite sides of the
transfer gear.
Inventors: |
Perry; Francine J. (Ottumwa,
IA), Chobhe; Shirish (Pune, IN), Rotole; David
V. (Bloomfield, IA) |
Assignee: |
Deere & Company (Moline,
IL)
|
Family
ID: |
42677234 |
Appl.
No.: |
12/399,071 |
Filed: |
March 6, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100224434 A1 |
Sep 9, 2010 |
|
Current U.S.
Class: |
180/403; 180/420;
280/87.2 |
Current CPC
Class: |
B62D
11/24 (20130101); B62D 7/06 (20130101); A01D
34/82 (20130101) |
Current International
Class: |
B62D
5/06 (20060101) |
Field of
Search: |
;180/403,417,420
;280/87.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hurley; Kevin
Claims
The invention claimed is:
1. A work machine, comprising: a frame; at least one drive wheel
carried by said frame; at least one caster wheel assembly carried
by said frame; at least one turn assist cylinder, each said turn
assist cylinder coupled between said frame and a corresponding said
caster wheel assembly; and a turn assist arrangement, including: a
steering assembly including an output gear which is positionable
dependent upon an operator commanded degree of turn; a steering
assist valve configured to selectively operate at least one said
turn assist cylinder and thereby bias said corresponding caster
wheel assembly during an operator commanded turn, said steering
assist valve including an input gear; and a transfer gear directly
interconnecting said output gear with said input gear.
2. The work machine of claim 1, wherein said transfer gear includes
a first set of peripheral teeth enmeshed with said output gear and
a second set of peripheral teeth enmeshed with said input gear.
3. The work machine of claim 2, wherein said transfer gear pivots
about a common pivot point, and said first set of peripheral teeth
and said second set of peripheral teeth are each at a common radius
from said common pivot point on opposite sides of said transfer
gear.
4. The work machine of claim 3, wherein said output gear and said
input gear each have exterior teeth, and wherein said first set of
peripheral teeth and said second set of peripheral teeth are each
radially inwardly facing teeth.
5. The work machine of claim 3, wherein said transfer gear has a
pair of truncated sides on opposite sides of said transfer gear,
between said first set of peripheral teeth and said second set of
peripheral teeth.
6. The work machine of claim 5, wherein said transfer gear is
generally bow-tie shaped.
7. The work machine of claim 1, wherein said output gear is
connected to a steering wheel column.
8. The work machine of claim 1, wherein said input gear extends
from said steering assist valve, and said steering assist valve
includes a plurality of hydraulic hoses, each said hose being
fluidly coupled with a respective said turn assist cylinder.
9. The work machine of claim 1, wherein said at least one drive
wheel comprises a pair of drive wheels, and said steering assist
arrangement is one of: integral with a dual-path hydrostatic system
associated with said drive wheels; and a stand-alone hydraulic
circuit which is separate from said dual-path hydrostatic
system.
10. The work machine of claim 1, wherein said at least one turn
assist cylinder comprises two turn assist cylinders, each said turn
assist cylinder coupled between said frame and a corresponding said
caster wheel assembly.
11. A steering arrangement for a work machine, comprising: a frame;
at least one caster wheel assembly carried by said frame; and at
least one turn assist cylinder, each said turn assist cylinder
coupled between said frame and a corresponding said caster wheel
assembly; a turn assist arrangement, including: a steering assembly
including an output gear which is positionable dependent upon an
operator commanded degree of turn, said output gear having exterior
teeth; a steering assist valve configured to selectively operate at
least one said turn assist cylinder and thereby bias said
corresponding caster wheel assembly during an operator commanded
turn, said steering assist valve including an input gear with
exterior teeth; and a transfer gear including a first set of
peripheral teeth enmeshed with said output gear and a second set of
peripheral teeth enmeshed with said input gear, said transfer gear
pivoting about a common pivot point, said first set of peripheral
teeth and said second set of peripheral teeth each being at a
common radius from said common pivot point on opposite sides of
said transfer gear.
12. The work machine of claim 11, wherein said first set of
peripheral teeth and said second set of peripheral teeth are each
radially inwardly facing teeth.
13. The work machine of claim 11, wherein said transfer gear has a
pair of truncated sides on opposite sides of said transfer gear,
between said first set of peripheral teeth and said second set of
peripheral teeth.
14. The work machine of claim 13, wherein said transfer gear is
generally bow-tie shaped.
15. The work machine of claim 11, wherein said output gear is
connected to a steering wheel column.
16. The work machine of claim 11, wherein said input gear extends
from said steering assist valve, and said steering assist valve
includes a plurality of hydraulic hoses, each said hose being
fluidly coupled with a respective said turn assist cylinder.
17. The work machine of claim 11, wherein said at least one drive
wheel comprises a pair of drive wheels, and said steering assist
arrangement is one of: integral with a dual-path hydrostatic system
associated with said drive wheels; and a stand-alone hydraulic
circuit which is separate from said dual-path hydrostatic
system.
18. The work machine of claim 11, wherein said at least one turn
assist cylinder comprises two turn assist cylinders, each said turn
assist cylinder coupled between said frame and a corresponding said
caster wheel assembly.
Description
FIELD OF THE INVENTION
The present invention relates to work machines, and, more
particularly, to a steering arrangement for steering such work
machines.
BACKGROUND OF THE INVENTION
Work machines may sometimes include one or more caster wheels which
are carried by a machine frame and free to rotate about a generally
vertical axis 360.degree.. The caster wheel assembly typically
includes a shaft defining an axis of rotation, a fork rigidly
attached to the bottom end of the shaft, and a caster wheel coupled
with the distal ends of the fork. Examples of such work machines
include windrowers, combines, lawn mowers, etc.
Self-propelled windrowers are typically driven through a dual-path
hydrostatic system. Speed changes are made by adjusting the speed
of both drive (front) wheels simultaneously. Direction changes are
made by adjusting the relative speed of the drive wheels. The rear
wheels of the machine are castered to allow the machine to pivot
during direction changes.
When direction changes are made, hydraulic pressure builds in one
drive wheel circuit to increase speed and is reduced in the other
drive wheel circuit to lower the speed. This relative pressure
difference prevails until the inertia of the machine and the
inherent turn resistance of the casters is overcome. If the turn
resistance is high enough to produce a noticeable delay in the
reaction to the steering wheel input, control of the machine can be
difficult.
Turn resistance of the caster wheels results from friction in the
pivot of the caster assembly and friction between the castered
wheels and the ground. Reaction delay can be particularly
pronounced if the machine is operated without the cutting platform
because the added weight on the casters results in increased turn
resistance. Low inflation pressures (e.g., 14 psi) are often
specified in the castered tires to improve ride quality. This
further increases turn resistance if the machine is operated with
the platform removed.
Steering characteristics are dependent on such things as steering
linkages, hydrostatic pump reaction time, the machine's turning
inertia, and caster turn resistance. There is a tendency for a
steering input to have a slow reaction (understeer) at initiation,
then a tendency to keep turning (oversteer) when the input is
stopped or reversed. Because of this, control of the machine can be
difficult, particularly at higher speeds. Windrowers typically have
a maximum speed in transport in the 15 mph range. Transport speeds
up to 25 miles per hour (mph) would be an advantage in the market.
This requires better machine controllability at higher speeds
without sacrificing the agility of the current system (spin steer)
at lower speeds.
It is known to provide a turn assist arrangement for the rear
caster wheels on a work machine. To that end, reference is hereby
made to U.S. patent application Ser. No. 11/957,800, entitled
"STEERING ASSIST FOR A REAR CASTER WHEEL ON A WORK MACHINE", filed
on Dec. 17, 2007, which is assigned to the assignee of the present
invention and incorporated herein by reference (hereinafter the
'800 application). With a turn assist arrangement as disclosed in
the '800 application, a steering assist valve which controls a flow
of hydraulic oil to the pair of steering assist cylinders is
coupled directly to the steering wheel column. Typically the
operator's cab is positioned in close proximity overlying the frame
of the work machine, and the space available for the steering
assist valve can be very limited.
What is needed in the art is a steering assist arrangement for a
work machine having rear caster wheels with improved versatility to
accommodate tight space restrictions.
SUMMARY OF THE INVENTION
The invention in one form is directed to a work machine including a
frame, at least one drive wheel carried by the frame, at least one
caster wheel assembly carried by the frame, at least one turn
assist cylinder, and a turn assist arrangement. Each turn assist
cylinder is coupled between the frame and a corresponding caster
wheel assembly. The turn assist arrangement includes a steering
assembly having an output gear, a steering assist valve and a
transfer gear. The output gear is positionable dependent upon an
operator commanded degree of turn. The steering assist valve is
configured to selectively operate at least one turn assist cylinder
and thereby bias the corresponding caster wheel assembly during an
operator commanded turn. The steering assist valve includes an
input gear. The transfer gear directly interconnects the output
gear with the input gear.
The invention in another form is directed to a steering arrangement
for a work machine including a frame, at least one caster wheel
assembly carried by the frame, at least one turn assist cylinder,
and a turn assist arrangement. Each turn assist cylinder is coupled
between the frame and a corresponding caster wheel assembly. The
turn assist arrangement includes a steering assembly, a steering
assist valve and a transfer gear. The steering assembly includes an
output gear which is positionable dependent upon an operator
commanded degree of turn. The output gear has exterior teeth. The
steering assist valve is configured to selectively operate at least
one turn assist cylinder and thereby bias a corresponding caster
wheel assembly during an operator commanded turn. The steering
assist valve includes an input gear with exterior teeth. The
transfer gear includes a first set of peripheral teeth enmeshed
with the output gear and a second set of peripheral teeth enmeshed
with the input gear. The transfer gear pivots about a common pivot
point. The first set of peripheral teeth and the second set of
peripheral teeth are each at a common radius from the common pivot
point on opposite sides of the transfer gear.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a portion of a work machine
incorporating an embodiment of a turn assist arrangement of the
present invention;
FIG. 2 is a top view of the portion of the work machine shown in
FIG. 1;
FIG. 3 is a schematic illustration of an embodiment of a turn
assist arrangement of the present invention;
FIG. 4 is a perspective view of the turn assist arrangement shown
in FIG. 3;
FIG. 5 is another perspective view of the turn assist arrangement
shown in FIG. 4; and
FIG. 6 is yet another perspective view of the turn assist
arrangement shown in FIGS. 4 and 5, with the top plate removed.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, and more particularly to FIGS. 1-3,
there is shown a portion of a work machine 10 incorporating an
embodiment of a turn assist arrangement 12 of the present
invention. Work machine 10 can be any type of self-propelled work
machine using one or more caster wheels, such as a windrower,
combine, lawn mower, etc. In the embodiment shown, the left rear
portion of a work machine in the form of a windrower 10 is shown
for illustration.
Windrower 10 includes a frame 14 carrying typical components (not
shown) such as an operator's station, internal combustion engine,
etc. A cutting platform is typically detachably mounted at the
front end of the machine below the operator's station. The engine
compartment is typically mounted behind the operator's station and
above a pair of caster wheel assemblies 16. Only the left rear
caster wheel 16 is shown in FIGS. 1 and 2 for simplicity, the right
rear caster wheel being configured substantially identical in the
illustrated embodiment. Some differences in the configurations of
the caster wheel assemblies 16 are possible, as will be described
in more detail below.
Each caster wheel assembly 16 includes a pivotable shaft 18, a
wheel arm 20 and a caster wheel 22 coupled with wheel arm 20. Shaft
18 is rotatably carried within a collar 24 which is welded or
otherwise rigidly affixed to frame 14. As shown in FIG. 1, the
machine frame 14 may include a telescoping axle having an outboard
end carrying collar 24. Wheel arm 20 is shown as a single arm which
curves around to the side of wheel 22, thus putting wheel 22
generally in line with shaft 18. Wheel arm 20 can also be
configured as a fork with distal ends on opposite sides of wheel
22. The lower or distal end of wheel arm 20 carries a stub shaft
26, which in turn carries a wheel hub 28 for mounting wheel 22 in
known fashion.
Caster wheel assembly 16 shown in FIGS. 1 and 2 is just one type of
caster wheel assembly that can be used with the present invention.
Further details of caster wheel assembly 16, as well as a
description of other non-inclusive types of caster wheel
arrangements which can be used with the present invention are
described in greater detail in the '800 application referenced
above.
Windrower 10 includes a linear actuator to be described in more
detail hereinafter, but may also be configured as a rotary or other
type actuator, as will become more apparent hereinafter. Windrower
10 includes one or more turn assist cylinders 30 which are coupled
between frame 14 and a corresponding caster wheel assembly 16. In
the embodiment shown, windrower 10 has two turn assist cylinders 30
coupled to respective caster wheel assemblies. Each turn assist
cylinder 30 biases a corresponding caster wheel assembly 16 during
an operator commanded turn.
Each turn assist cylinder 30 is in the form of a two-way cylinder
with a housing 32 defining an inner chamber 34, a piston 36
slidably disposed in inner chamber 34, and a rod 38 extending from
piston 36 through housing 32 (interior components of turn assist
cylinder 30 are shown in phantom lines in FIG. 2). Housing 32 is
carried by mounting plates 14A, which are considered for practical
purposes to be part of frame 14. In the embodiment shown, each turn
assist cylinder 30 also includes a second rod 40 extending from
piston 36 through housing 32. Rod 38 and second rod 40 are disposed
on opposite sides of piston 36, with second rod 40 providing an
equal fluid displacement from inner chamber 34 regardless of a
travel direction of piston 36. It will be understood, however, that
a single piston rod 38 may be utilized.
Windrower 10 is shown with a pair of turn assist cylinders 30, with
each turn assist cylinder 30 being coupled between frame 14 and a
corresponding caster wheel assembly 16. However, it is also
possible to configure windrower 10 with a single turn assist
cylinder 30 coupled between frame 14 and one caster wheel assembly
16, the other caster wheel being free turning. Alternatively,
windrower 10 may be configured with a single turn assist cylinder
30 coupled between frame 14 and one caster wheel assembly 16, the
one caster wheel assembly being coupled via a tie rod or the like
with the other caster wheel assembly.
Windrower 10 also includes a pivot arm 42 associated with each
caster wheel shaft 18, and a ball linkage 44 interconnecting each
piston rod 38 with a corresponding pivot arm 42. Pivot arm 42 is
rigidly affixed to and extends radially outward from the top end of
shaft 18 and rotates or pivots therewith, such as through a
suitable keyed connection. The length of pivot arm 42 may be
selected dependent upon the desired amount of turn assist force,
etc. Pivot arm 42 has an opposite, distal end which is coupled with
one end of ball linkage 44, which in turn has an opposite end which
is coupled with the outer end of piston rod 38. Ball linkage 44 may
have an adjustable length using a threaded rod and lock nut
arrangement, as shown. Windrower 10 is thus configured with a
stroke length of rod 38, ball linkage 44 and pivot arm 42 allowing
full 360 degree rotational movement of caster wheel 22 about the
axis of shaft 18. This may be important when changing directions of
windrower 10 from forward to reverse, or vice versa, or for side
loads applied to wheel 22 due to ground terrain variations,
etc.
Referring now to FIG. 3, there is shown a schematic illustration of
turn assist arrangement 12 for caster wheels 22. Turn assist
arrangement 12 includes a hydraulic steering circuit 46. Turn
assist cylinders 30 are coupled in series using a fluid tie rod
arrangement. A pair of direction change valves 48 are coupled in
parallel with a corresponding turn assist cylinder 30, and a
proportional valve 50 is connected in parallel between turn assist
cylinders 30. Proportional valve 50 is open at lower ground speeds
to allow free parallel movement of turn assist cylinders 30.
Proportional valve 50 begins to close at approximately the same
speed as direction change valves 48 close. Proportional valve 50
closes proportional to increasing speed, then remains closed at
higher speeds. Proportional valve 50 softens the transition between
the dual path hydrostatic system at low speeds and the rear steer
system turn assist at higher transport speeds.
Referring now to FIGS. 4-6, conjunctively, hydraulic steering
circuit 46 generally includes a steering assembly 52, steering
assist valve 54, and transfer gear 56. Steering assembly 52
includes a spline shaft 58 and an output gear 60. Spline shaft 58
is directly coupled with the bottom end of a steering wheel column
having an operator input with an angular orientation corresponding
to a desired direction of travel of windrower 10. The steering
wheel column also provides output signals for control of respective
drive wheel motors 61, each coupled with and driving a
corresponding drive wheel 63. Output gear 60 is rigidly attached to
the bottom end of spline shaft 58, and is likewise positionable
dependent upon an operator commanded degree of turn. Output gear 60
has a plurality of exterior teeth (not individually numbered) with
a tooth profile that can vary depending on the application.
Steering assist valve 54 includes a number of hydraulic hoses 62
which may be respectively coupled with a corresponding turn assist
cylinder 30. Steering assist valve 54 is configured to selectively
operate the turn assist cylinders 30 and thereby bias a
corresponding caster wheel assembly 16 during an operator commanded
turn. Steering assist valve 54 includes an input gear 64 with a
plurality of exterior teeth with a predetermined tooth profile
depending upon the application.
Transfer gear 56 generally is in the form of a large gear which
pivots about a common pivot point 66, and has a pair of truncated
sides 68 on opposite sides thereof (with the truncated portion of
the circular gear being shown in dashed lines in FIG. 3). Transfer
gear 56 functions to interconnect output gear 60 with input gear 64
located at a position away from steering assembly 52. The
arrangement of transfer gear 56 allows steering assist valve 54 to
be located other than directly underneath steering assembly 52,
thereby allowing an increased size and displacement volume of
steering assist valve 54.
Transfer gear 56 includes a first set of peripheral teeth 70 which
enmesh with output gear 60, and a second set of peripheral teeth 72
which enmesh with input gear 64. The first set of peripheral teeth
70 and second set of peripheral teeth 72 are disposed on opposite
sides of transfer gear 56, with the truncated sides 68 extending
therebetween. In FIG. 3, the first set of peripheral teeth 70 and
second set of peripheral teeth 72 are each shown as exterior teeth
enmeshed with the corresponding output gear 60 and input gear 64.
In another embodiment shown in FIGS. 4-6, the first set of
peripheral teeth 70 and second set of peripheral teeth 72 are each
shown as radially inwardly facing teeth which enmesh with the
outside of the corresponding output gear 60 and input gear 64.
Configured as shown in FIGS. 4-6, transfer gear 56 is generally
bow-tie shaped. Of course, it is also possible to have one of a set
of peripheral teeth 70 or 72 as exterior teeth, and the other of a
set of peripheral teeth 70 or 72 as radially inwardly facing
teeth.
Transfer gear 56 is also used in the control of drive wheels 63. A
linkage 74 which pivots about pivot point 66 pivots concurrently
with transfer gear 56 (FIGS. 4 and 6). Linkage 74 is coupled via an
intermediate linkage 76 with a pump control rod 78 used to control
the flow of hydraulic fluid to drive wheel motors 61. The
differential flow of hydraulic fluid to drive wheel motors 61
provides propulsion and primary turning of windrower 10 using drive
wheels 63.
During operation of windrower 10, hydraulic steering assembly 52
controls operation of the dual path hydrostatic drive to drive
wheel motors 61 in known manner. Concurrently, steering assembly 52
pivots transfer gear 56 about pivot point 66, depending upon the
position of the steering wheel. Transfer gear 56 in turn rotates
input gear 64 to control operation of turn assist cylinders 30.
Having described the preferred embodiment, it will become apparent
that various modifications can be made without departing from the
scope of the invention as defined in the accompanying claims.
* * * * *